Aims: The purpose of the present study was to investigating relationship between perceptual strain index (PeSI) with indices heat strain score (HSSI), wet bulb globe temperature (WGBT) in experimental hot condition. Materials and Methods: This study in five different temperature conditions (21°C, 24°C, 27°C, 30°C, and 35°C) was carried out on 15 male students in the climate chamber and on the treadmill with three levels of the activity. The thermal sensation and perceived exertion was recorded for calculating PeSI, and HSSI questionnaire was completed. Results: Pearson correlation test showed a high correlation (r = 0.84) between the PeSI and HSSI (P = 0.001). Also, Pearson correlation test showed between PeSI with WBGT and air temperature, respectively, a good correlation (r = 0.76) and high correlation (r = 0.81) (P = 0.001). Conclusion: The findings of the study showed that the PeSI can be used for evaluating heat strain in the absence of access to other methods of evaluating heat stress since it has an acceptable correlation with valid indices of heat stress. Also, easy application and quick and cost is much less than other evaluating heat strain indices.